Computed Radiography (CR) imaging systems form images by directing X-rays through a subject and onto a photostimulable phosphor storage medium. To obtain the image stored thereon, the stimulable phosphor storage medium is then processed by a scanner that scans a laser beam or other light source across the surface of the storage medium, releasing the stored charge for each pixel (picture element) of the image. The charge that is thus obtained is indicative of the image that was originally stored from X-ray radiation. Advantageously, the stimulable phosphor medium can be repeatedly erased and re-used.
In conventional CR systems, designed to be compatible with the film-based model of earlier X-ray imaging apparatus, the photostimulable phosphor storage medium is a plate or flexible sheet that is stored within a cassette. The cassette allows the phosphor sheet to be placed into position, imaged, and processed without the need for an operator or technologist to touch and possibly degrade the storage medium. The scanner then extracts the phosphor plate or sheet from the protective cassette, scans the sheet by transporting it across a scan head that contains the scanning light source used for photostimulation, and restores the phosphor storage medium to its cassette.
In the conventional scanning paradigm, the image scanning device is typically designed for the specific characteristics of the type of stimulable phosphor storage medium that is used. Thus, for example, a scanner may be designed to handle phosphor plates of given dimensions and other physical characteristics and is typically able to process only those plates packaged in a specific cassette configuration. Similarly, a scanner for flexible media requires that the scanned phosphor sheet at least have a standard width, or a width that is compatible with its transport drive system. This standard approach is satisfactory for some types of systems. However, restricting media dimensions to a certain specific size or range of sizes presents a limitation for some types of imaging. In particular, non-destructive testing (NDT) applications benefit by imaging onto sections of flexible phosphor sheet that can be inserted into an orifice or wrapped about a weld or other structure. The sections of imaging medium that are needed for such applications may be cut to irregular size or may be too small for processing in a conventional scanner having a sheet transport apparatus.
Because of these limitations of scanner transport, the conventional solution for imaging using odd-sized sections of flexible photostimulable storage media uses a flatbed scanner. An oddly shaped or smaller sized section of a phosphor imaging medium can be simply laid flat against the platen of the flatbed scanner and pressed beneath the scanner cover for obtaining the image. While this presents a workable solution, however, the need to procure, store, and use a separate flatbed scanning device for NDT imaging adds to the cost, complexity, and space required for such systems. In many cases, the scanner platen height and width dimensions may far exceed those of the scanned medium.
Thus, it can be seen that there is a need for a mechanism that allows flexible phosphor storage medium to be transported through a sheet-fed scanner.